In the aerospace industry, the use of composites is becoming ever more important as a large number of primary and secondary structures in aircraft frames being made of composite materials. The advantages of composites in aircraft designs include high strength-to-weight ratio, excellent fatigue endurance, corrosion resistance and flexibility, allowing a significant reduction in component parts and the need for fasteners and joints. However, the application of these materials to modern aircraft's primary and secondary structures presents special challenges due to the dielectric nature of the resin matrix. Although the use of carbon fibres as reinforcing fibres in composite materials can deliver some degree of electrical conductivity along their longitudinal direction due to their graphitic nature, the dielectric properties of the matrix resins in the composite materials reduce the overall electrical conductivity of the composite materials and structures. Composites with increased electrically conductivity are required for aircraft primary structures to satisfy stringent requirements for lightning strike protection, potential discharge, electrical grounding and electromagnetic shielding.
The electrical conductivity of resins and composites can be improved by incorporating different conductive particles or polymers in the resin matrix or in the interlaminar regions of the composite structures. Such state of the art material solutions can be used to improve the z-direction conductivity of a composite but not its mechanical performance. The “z-direction” refers to the direction orthogonal to the planes on which the reinforcing fibres are arranged in a composite structure or the axis through the thickness of the composite structure.